In situ assembled mass-transport controlling micromembranes and their application in implanted amperometric glucose sensors

Micromembranes were assembled by sequentially chemisorbing polyanions and p olycations on miniature (5 x 10(-4) cm(2)) enzyme electrodes. The sequentia l chemisorption process allowed the simultaneous tailoring of their sensiti vity, dynamic range, drift, and selectivity. When assembled on tips of 250- mu m-diameter gold wires coated with redox polymer-"wired" glucose oxidase, they allowed tailoring of the glucose electrodes for >2 nA/mM sensitivity; 0-30 mM dynamic range; drift of less than or equal to 5% per 24 h at 37 de grees C at 15 mM glucose concentration; and 15% current increment by the co mbination of 0.1 mM ascorbate, 0.2 mM acetaminophen, and 0.5 mM urate, The membranes also retained transition metal ions that bound to and damaged the redox polymer "wiring" the enzyme. The electrodes were tested in the jugul ar veins and in the intrascapular subcutaneous region of anaesthetized and heparinized nondiabetic Sprague-Dawley rats, in which rapid changes of glyc emia were forced by intravenous injections of glucose and insulin. After on e-point in vivo calibration of the electrodes, all of the 152 data points w ere clinically accurate when it was assumed that after insulin injection th e glycemia in the subcutaneous fluid lags by 9 min behind that of blood wit hdrawn from the insulin-injected vein.